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Maneuvering Boards Review
Maneuvering Boards Review
• AGENDA:
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Definition of Relative Motion
True Bearings vs. Relative Bearings
The Maneuvering Board
The Relative Plot
Application: Example of Collision
Avoidance (CPA)
True vs. Relative Motion
True vs Relative Motion: Understanding
the difference between true and relative
motion is essential in excelling in
moboards.
– True Motion: the movement of an object
with respect to the surface of the earth.
– Relative Motion: the apparent movement of
an object with respect to another moving
object.
Relative Movement
• Represented on maneuvering board
– Consider yourself onboard ship monitoring
actions of other ships
– Find actual course and speed required to
bring about desired change in relative
position in maneuvering a ship at sea
True vs. Relative Bearings
• Line of Sight (LOS) = straight line between an
observer and an object.
• True Bearings (T) = direction measured with
respect to true of geographic north.
• Ship’s heading (°T)
• Relative Bearings (R) = direction measured
with reference to the ship’s longitudinal axis.
Line of Sight
• Each line of sight has two directions
which differ by 180 degrees
• Heading of either ship does not affect the
LOS
True Bearings
• True Bearing - bearing measured
clockwise from true north in degrees to
line of sight
• heading of ship does not affect
bearing
• reference line true north remains
same regardless of movement
TRUE BEARINGS
N
000T
Ship’s course =
045T
W
?
E
090T
135T
S
Relative Bearings
•
Relative Bearing - measured in degrees
from ships heading (course) clockwise
to the observed object
–
Remember - course of reference ship will
always affect relative bearing because it is
reference line for relative bearing
Remember…
• Never plot relative bearings on a
maneuvering board
• Must convert relative bearings to true
bearings before plotting
RELATIVE BEARING
N
270R
E
W
090T
180R
000R
090R
180 T
S
RELATIVE
N
BEARINGS
Ship’s course =
045T
?
W
E
?
135T
S
RELATIVE
N
BEARINGS
Ship’s course =
045T
000R
W
E
180R
135T
S
Converting True and
Relative Bearings
• Converting relative bearing to true is
accomplished by using the following
formula:
TB = SH + RB
• Example: Contact bears 270°R, ship is on course
330°T. What is the true bearing to the contact?
TB = SH + RB
TB = 330° + 270°
TB = 600°  240°T
The Maneuvering Board
• Purpose: a tool to plot the position of a ship
relative to the position of another ship.
• Applications:
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Collision Avoidance …
Formation Steaming …
RDVU/Intercept …
Wind Problems …
CPA’s
Station Keeping
UNREP’s
Desired wind
The Maneuvering
Board
• Description:
– Ten concentric circles
– Bearing lines radiating
from the center.
– Five scales provided.
– Nomogram provided.
The Relative Plot
• Relative Plot: Defined as a polar
representation of the successive positions
of one or more moving objects with
respect to a reference position. This
reference position will normally be your
own vessel; the bearings and ranges are
taken from your radar.
The Relative Plot
• The maneuvering board (relative plot).
– E - reference ship (placed in the center)
– M1, M2 - any maneuvering ship
– DRM - Direction of Relative Motion
– MRM - Measure of Relative Motion
– SRM - Speed of Relative Motion
– CPA - Closest Point of Approach
Closest Point of Approach (CPA)
• Made up of three parts
– Range/Distance
– Bearing
– Time
Setting up a MoBoard
• First Determine Scale
– Speed
– Distance
D
S
Setting up a MoBoard
• Second plot yourself in the center of the
MoBoard
• Then plot your ship’s
– Speed
– Distance
– For Example you are on a course of 050T at
a speed of 15 kts.
D
S
r
e
Example: CPA
Determining CPA:
At 0800 a contact bears 280ºT, at a range of
16,000 yards.
1. Plot M1(points on the moboard the correspond to
the bearings and ranges of the contact)- note, use
a 2:1 scale.
D
S
r
M1
e
Example: CPA
Determining CPA:
At 0815 the same contact bears 300ºT, at 10,000
yards. Find the CPA (bearing, range, and time):
1. Plot M1 and M2 (points on the moboard the
correspond to the bearings and ranges of the
contact)- note, use a 2:1 scale.
D
S
M2
M1
r
e
Example: CPA
Determining CPA:
At 0800 a contact bears 280ºT, at a range of
16,000 yards. At 0815 the same contact bears
300ºT, at 10,000 yards. Find CPA bearing, range,
and time:
1. Plot M1 and M2 (points on the moboard the
correspond to the bearings and ranges of the
contact)- note, use a 2:1 scale.
2. Find DRM - 073ºT
D
S
M2
M1
r
e
Example: CPA
Determining CPA:
At 0800 a contact bears 280ºT, at a range of
16,000 yards. At 0815 the same contact bears
300ºT, at 10,000 yards. Find CPA bearing, range,
and time:
1. Plot M1 and M2 (points on the moboard the
correspond to the bearings and ranges of the
contact)- note, use a 2:1 scale.
2. Find DRM - 073ºT
3. Find MRM - 7,500 yards
D
S
MRM
M2
M1
r
e
Example: CPA
Determining CPA:
At 0800 a contact bears 280ºT, at a range of
16,000 yards. At 0815 the same contact bears
300ºT, at 10,000 yards. Find CPA bearing, range,
and time:
4. Enter nomogram with 7,500 yards and 15
minutes (elapsed time between interval 0800 to 0815) to find SRM - 15 knots
D
S
MRM
M2
M1
r
e
Example: CPA
Determining CPA:
At 0800 a contact bears 280ºT, at a range of
16,000 yards. At 0815 the same contact bears
300ºT, at 10,000 yards. Find CPA bearing, range,
and time:
4. Enter nomogram with 7,500 yards and 15 minutes
(elapsed time between interval - 0800 to 0815) to
find SRM - 15 knots
5. CPA bearing (Add or subtract 90 to/from DRM to
determine CPA Bearing) - in this case subtract 90:
073ºT - 090ºT = 343ºT
D
S
343T
MRM
90
r
M2
M1
e
Example: CPA
Determining CPA:
At 0800 a contact bears 280ºT, at a range of
16,000 yards. At 0815 the same contact bears
300ºT, at 10,000 yards. Find CPA bearing, range,
and time:
6. CPA Range - measure from the center of the
maneuvering board to CPA point to determine
CPA range - 7,500 yards
D
S
MRM
CPA Range
M2
M1
r
e
Example: CPA
Determining CPA:
At 0800 a contact bears 280ºT, at a range of
16,000 yards. At 0815 the same contact bears
300ºT, at 10,000 yards. Find CPA bearing, range,
and time:
7. CPA Time - measure the distance between M2 &
CPA point. This distance is 6,900 yards. Enter
the nomogram with 6,900 yards and an SRM of
15 knots - 14 minutes (add this to time of M2 to
find CPA time)
D
S
MRM
CPA Range
M2
M1
r
e
Questions?